Sentinel-6 MF Poseidon-4 Radar Altimeter In-Flight Calibration and Performances Monitoring

Abstract

Poseidon-4 is a dual frequency redundant radar altimeter, embarked on board the Sentinel-6 Michael Freilich European Commission Copernicus Programme satellite. In this paper, we assess Poseidon-4 main instrumental improvements and performances, with the presentation of the more important outcomes from the In-Flight internal calibration modes and from an external calibration analysis over a transponder. The instrumental performances of the radar altimeter are excellent for both radar chain sides: Poseidon-4 delivers a range/azimuth instrument impulse response with the highest quality and fidelity in the era of space-borne radar altimetry and its thermal noise response is almost just random noise. A power decay of the level of the transmitted power in Ku-Band has been detected both for the nominal and for redundant sides, which is larger than expected though will not violate the requirement of the minimum signal-to-noise ratio over ocean at the end of the satellite design lifetime. The innovative CAL1 ECHO CAL calibration mode allows to characterize very precisely the sensitivity of the instrument impulse response to the in-orbit temperature variations and thus correct for it in the science data as standard practice.